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https://github.com/torvalds/linux
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959f5f5b2f
Suppose that a system has two CPU sockets, three cores per socket, that it does not support hyperthreading and that four hardware queues are provided by a block driver. With the current algorithm this will lead to the following assignment of CPU cores to hardware queues: HWQ 0: 0 1 HWQ 1: 2 3 HWQ 2: 4 5 HWQ 3: (none) This patch changes the queue assignment into: HWQ 0: 0 1 HWQ 1: 2 HWQ 2: 3 4 HWQ 3: 5 In other words, this patch has the following three effects: - All four hardware queues are used instead of only three. - CPU cores are spread more evenly over hardware queues. For the above example the range of the number of CPU cores associated with a single HWQ is reduced from [0..2] to [1..2]. - If the number of HWQ's is a multiple of the number of CPU sockets it is now guaranteed that all CPU cores associated with a single HWQ reside on the same CPU socket. Signed-off-by: Bart Van Assche <bvanassche@acm.org> Reviewed-by: Sagi Grimberg <sagig@mellanox.com> Cc: Jens Axboe <axboe@fb.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Ming Lei <ming.lei@canonical.com> Cc: Alexander Gordeev <agordeev@redhat.com> Signed-off-by: Jens Axboe <axboe@fb.com>
119 lines
2.5 KiB
C
119 lines
2.5 KiB
C
/*
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* CPU <-> hardware queue mapping helpers
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*
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* Copyright (C) 2013-2014 Jens Axboe
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*/
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#include <linux/kernel.h>
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#include <linux/threads.h>
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#include <linux/module.h>
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#include <linux/mm.h>
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#include <linux/smp.h>
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#include <linux/cpu.h>
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#include <linux/blk-mq.h>
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#include "blk.h"
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#include "blk-mq.h"
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static int cpu_to_queue_index(unsigned int nr_cpus, unsigned int nr_queues,
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const int cpu)
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{
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return cpu * nr_queues / nr_cpus;
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}
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static int get_first_sibling(unsigned int cpu)
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{
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unsigned int ret;
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ret = cpumask_first(topology_thread_cpumask(cpu));
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if (ret < nr_cpu_ids)
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return ret;
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return cpu;
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}
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int blk_mq_update_queue_map(unsigned int *map, unsigned int nr_queues)
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{
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unsigned int i, nr_cpus, nr_uniq_cpus, queue, first_sibling;
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cpumask_var_t cpus;
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if (!alloc_cpumask_var(&cpus, GFP_ATOMIC))
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return 1;
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cpumask_clear(cpus);
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nr_cpus = nr_uniq_cpus = 0;
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for_each_online_cpu(i) {
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nr_cpus++;
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first_sibling = get_first_sibling(i);
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if (!cpumask_test_cpu(first_sibling, cpus))
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nr_uniq_cpus++;
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cpumask_set_cpu(i, cpus);
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}
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queue = 0;
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for_each_possible_cpu(i) {
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if (!cpu_online(i)) {
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map[i] = 0;
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continue;
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}
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/*
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* Easy case - we have equal or more hardware queues. Or
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* there are no thread siblings to take into account. Do
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* 1:1 if enough, or sequential mapping if less.
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*/
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if (nr_queues >= nr_cpus || nr_cpus == nr_uniq_cpus) {
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map[i] = cpu_to_queue_index(nr_cpus, nr_queues, queue);
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queue++;
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continue;
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}
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/*
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* Less then nr_cpus queues, and we have some number of
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* threads per cores. Map sibling threads to the same
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* queue.
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*/
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first_sibling = get_first_sibling(i);
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if (first_sibling == i) {
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map[i] = cpu_to_queue_index(nr_uniq_cpus, nr_queues,
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queue);
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queue++;
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} else
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map[i] = map[first_sibling];
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}
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free_cpumask_var(cpus);
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return 0;
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}
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unsigned int *blk_mq_make_queue_map(struct blk_mq_tag_set *set)
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{
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unsigned int *map;
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/* If cpus are offline, map them to first hctx */
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map = kzalloc_node(sizeof(*map) * nr_cpu_ids, GFP_KERNEL,
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set->numa_node);
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if (!map)
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return NULL;
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if (!blk_mq_update_queue_map(map, set->nr_hw_queues))
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return map;
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kfree(map);
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return NULL;
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}
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/*
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* We have no quick way of doing reverse lookups. This is only used at
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* queue init time, so runtime isn't important.
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*/
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int blk_mq_hw_queue_to_node(unsigned int *mq_map, unsigned int index)
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{
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int i;
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for_each_possible_cpu(i) {
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if (index == mq_map[i])
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return cpu_to_node(i);
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}
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return NUMA_NO_NODE;
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}
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